A private investigator with a criminal past says he’s willing to spill his guts about how to score fake passports — but the feds aren’t interested.

Oded Daniel Gal who was sentenced to four years in prison after being convicted in 1992 for hiring two thugs to rough up John Wayne’s daughter, copped a plea Friday in Manhattan federal court to obtaining a bogus passport nine years ago.

During the hearing, Gal’s lawyer, Timothy Parlatore, revealed to Judge Paul Engelmayer that his client was rejected by Manhattan federal prosecutors after offering to share research he pooled together from various underworld sources about current methods being used to obtain fake passports.

When approached by The Post afterwards, Parlatore and Gal said they were perplexed by the Manhattan US Attorney’s Office’s refusal to listen to details about how “terrorists and other criminals” right under the government’s nose are able to beat facial-recognition software and other investigative techniques.

“Everybody is worried about bad guys coming into this country,” said Gal, 58. “And based on the way the passport applications are, there are methods out there that the government won’t detect until it is too late.”